Benchmarking surface selective vacuum ultraviolet and thermal postprocessing of thermoplastics for ultrasmooth 3-D-printed micro-optics

Abstract

State-of-the-art, polymeric, refractive micro-optics simultaneously require an ultrasmooth threedimensional (3-D) surface and a precise geometry for excellent optical performance with minimal stray light. In earlier work, we have established a surface finishing process for thermoplastic polymer master structures that is only effective on the surface and does not affect the designed optical geometry, thus enabling polishing without touching. Therewith, the high curvature corners of a 50-μm-tall optical diffuser device were maintained while the surface roughness was reduced to about 10-nm root mean square. For this, 3-D master structures were first fabricated by direct write laser-lithography with two-photon polymerization. The master structures were replicated into poly(methyl methacrylate) through a poly(dimethyl siloxane) intermediate replication stamp. Finally, all structures were surface-polished by selective high-energy photon exposure and thermal postprocessing. In this work, we focus on the comparison of the surface smoothening using either postprocessing or dedicated direct writing strategies. For this comparison, strategies for modifying the exposed voxel size and the writing discretization being the primary source of roughness were tested by sweeping the laser exposure dose for two different resist materials and objectives. In conclusion, the postprocessing smoothening resulted in a lower roughness compared to a direct writing strategy-even when 50-nm vertical discretization steps were usedand still enabled 10 times shorter writing times.

Perspectives of reactive ion etching of silicate glasses for optical microsystems

“…Deep-etched vertical structure profiles with low surface roughness Ra of the sidewalls (below 10 nm in the visible range) are needed for high quality integrated optical modules. 73 Their fabrication from bulk substrates through surface micromachining requires a highly controlled deep etching process with stable etching masks, high selectivity, and high-quality edges.…”

3D-Printed Biosensor Arrays for Medical Diagnostics

“…3D-printed optical tweezers for sample trapping [ 125 ] were also developed to aid chemical and spectroscopic sample analysis. Some other 3D-printed fine optics that have not been used yet in diagnostics have also been proposed [ 126 , 127 ]. Integrating compact, lost-cost, effective optical components is a crucial development for POC diagnostics.…”

Mastering of NIL Stamps with Undercut T-Shaped Features from Single Layer to Multilayer Stamps

“…A nanostructured stamp is used to mechanically emboss a polymer layer on a substrate [11]. Such three-dimensionally structured surfaces are interesting for microfluidic channels [12,13], superhydrophobic surfaces [14], and optical applications [15,16]. Also undercut structures [11,17] and hierarchical structures [18] can be fabricated.…”